Involvement of a novel Pseudomonas protegens strain associated with entomopathogenic nematode infective juveniles in insect pathogenesis

Abstract

BACKGROUND:The bioinsecticidal action of entomopathogenic nematodes (EPNs) typically relies on their symbiosis with core bacteria. However, recent studies highlighted the possible involvement of other noncore species. We have recently isolated a novel Pseudomonas protegens strain as a major agent of septicaemia in larvae of the wax moth, Galleria mellonella, infected with a soil-dwelling Steinernema feltiae strain. The actual role of this bacterium in entomopathogenesis was investigated. RESULTS: The association of P. protegens with nematodes appeared to be robust, as supported by its direct and repeated isolation from both nematodes and insect larvae infected for several consecutive generations. The bacterium appeared to be well-adapted to the insect haemocoel, being able to proliferate rapidly after the injection of even a small amount of living cells [100 colony forming units (CFU)] to a larva, causing its fast death. The bacterium also was able to act by ingestion against G. mellonella larvae [median lethal concentration (LC 50 ) = 4.0 × 10 7 CFU mL -1 ], albeit with a slower action, which supports the involvement of specific virulence factors (e.g. chitinases, Fit toxin) to overcome the intestinal barrier to the haemocoel. Varying levels of bacterial virulence were observed on diverse target Diptera and Lepidoptera.CONCLUSION: The soil-dwelling bacterium P. protegens appears to have evolved its own potential as a stand-alone entomopathogen, yet the establishment of an opportunistic association with entomoparasitic nematodes would represent a special competitive advantage. This finding contributes to a deeper understanding of the nematode-bacteria biocontrol agent complex and the deriving paradigm of their use as biological control agents.

Structures and Biosynthesis of Caryoynencins, Unstable Bacterial Polyynes from Pseudomonas protegens Recombinant Expressing the cayG Gene

“…protegens Cab57, was not pathogenic on plants, such as B. caryophylli strains. − We expect that the usefulness of P. protegens Cab57 and its transformants can be further demonstrated by introducing other modifying enzymes for bacterial polyynes.…”

“…Pseudomonas protegens strains are well-known as biocontrol agents that protect crops from pathogens (e.g., fungi, oomycetes, and nematodes). − We recently identified new bacterial polyynes, protegenins A–D, from P. protegens Cab57 by genome mining (Figure A) .…”

The genome of a steinernematid-associated Pseudomonas piscis bacterium encodes the biosynthesis of insect toxins

“…Similarly, at 72 h post-infection with S. feltiae CO1, P. protegens was the dominant bacteria in haemolymph from G. mellonella cadavers [11]. Relatedly, in S. carpocapsae -infected Manduca sexta cadavers, X.…”

“…IJs seek out insect prey and gain entry into the haemocoel through either natural openings or by burrowing through the insect cuticle [5]. Once within the haemocoel, IJs release their bacterial symbionts which include Xenorhabdus, Pseudomonas, Alcaligenes, Stenotrophomonas, Serratia, Ochrobactrum, Enterobacter, Pseudochrobactrum, and Brevundimonas [6][7][8][9][10][11]. Upon detection of insect haemolymph, Xenorhabdus bacteria secrete [12] a pot pourri of natural products that ultimately contribute to both the fecundity and entomopathogenicity of their nematode host.…”

“… P. protegens C01 from S. feltiae was entomopathogenic to both lepidopterans and dipterans via both oral and intrahaemocoel routes [11]. The P.…”